Soundstage!- Greg Smith


October 1996

If you've been reading my Entry Level columns, you've noticed that I frequently talk about my speakers. Klipsch introduced a collection of designs they called the Heritage series back around the beginning of the decade, and the jewel in that collection is a model called the Forte II. Being from Klipsch, they use horns, but these speakers are the best designed horns I've ever heard for any reasonable sum of money. They've been out of production for many years now, so I haven't been pushing them too much. Imagine my surprise when I found out that Klipsch is making them again, and they're even cheaper than before! With the current craze, centered around things like single ended tubes, toward higher efficiency speakers, it's particularly appropriate to talk now about what these speakers do well and to mention some of the things I've learned in five years of system matching.

The Return of the Forte II
Klipsch Forte II

$1000/pair. Horn Tweeter, Tractrix Horn Midrange, 12 inch woofer, 15 inch passive radiator, crossover points at 650hz and 7Khz. 99dB sensitivity, 8 ohm nominal impedance, 4 ohm minimum. -3dB@32hz, 20Khz.

There are speakers that you just buy, plug in, and play. Sure, maybe you move them around a bit, but most speakers arenít all that difficult to get working well. These are not speakers like that. The Forte II is something you need to plan your whole system and room around to make it perform well. You donít just pick a random set of components, position them like regular cone speakers, and expect them to perform. The result will probably sound horrible. I will fully agree that most horn design sound horrible in any case, including many from Klipsch. The Forte II can be made to sound very good, but it takes quite a bit of sweat. Just because youíve heard horns before and thought they sounded bad, donít dismiss these.

Hereís one thing Iíve noticed about horn speakers. Because the efficiency is so high, itís much easier to use the drivers out of their normal operating range without causing over-excursion problems. This is why youíll find so many two-way horn designs. You can push most tweeter horns so that they work down to around 2Khz, and keep the frequency response fairly flat. Unfortunately, this results in a less than pleasant off-axis response at higher frequencies. The horn problem most people refer to as "honking" is most obvious with two-way horn designs, and Iíve never liked them because of it.

When the engineers at Klipsch were designing the Tractrix midrange horn that is used in the Forte II, they found it could be used up to 20Khz if they played with the EQ on the driver. They didnít do so; instead, there is a separate tweeter horn for the very high frequencies. Limiting the bandwidth used for the midrange horn lets it cover a horizontal area of 60 degrees smoothly while controlling the vertical coverage for better integration with the other drivers (see Tractrix Horns in the March 1991 issue of Audio for information how the Forte II was created). The fact that the midrange is so well designed is the primary reason this particular model sounds so much better than the other speakers Iíve heard from Klipsch, or from any other horn manufacturer for that matter.

The midrange is really what makes this speaker sound great. Thereís a totally effortless feeling to vocals that comes from a driver operating nowhere near its limits in either frequency response or output level. And the foundation that midrange is working on is very solid. The bass is tight down to 30hz if the associated electronics keep up. Youíll feel little need for a subwoofer.

And if you want peak output, youíve got it. Iíve measured my speakers clearing 115dB in my room before (with my ears covered, thank you). They sounded about as distorted as your average cone speakers do with 10dB less output (which is what youíd expect with a typical 10dB sensitivity difference). While I certainly donít recommend listening to anything that loud, itís nice to know you can use your speakers for low-grade sound reinforcement without constantly fearing damage. The low distortion makes the volume level deceptive; I can listen to these speakers at a considerably higher volume than more traditional designs without ear fatigue. Distortion makes speaker sound loud regardless of the volume, and itís surprising how much quieter the same volume levels sounds without it present (this is a central concept to Paul Klipschís philosophy for the company).

Amplifier matching

With that 99dB sensitivity, youíd think you could use any old amplifier and have plenty of power. This is not at all the case. In order to match the output levels of the drivers (those horns are even louder than that without some padding), Klipsch uses some very unique matching techniques using things like a type of transformer. (see A Visit to the Klipsch Kingdom in the 4/89 issue of Speaker Builder for comments from Paul Klipsch on their autoformer design). Transformers are obviously inductive, as they are made out of inductors. What this means is that while the amplifier used doesnít need to have a very high power output in typical terms, it does need to be able to deal with the very difficult load that inductors present. Using a cheap receiver to drive these speakers just because you donít need much power is the wrong approach. What you need is a high- current amplifier that can deal with difficult loads without introducing problems.

One of the problems youíll constantly fight with these speakers is that any components that might sound a bit harsh with other speakers will have that harshness revealed in all its glory. Use a typical cheap CD player and a pair of these speakers will drive you from the room. The amplifier matching in particular can introduce an incredibly rough sound. Back when I was using an Adcom GFA-555 with these speakers, an amplifier generally recognized as being a bit too aggressive in its treble, I had to deal with a level of sibilance that was almost unbearable. The Proton D1200 amplifier I current use is a very good match, but you canít buy them anymore. Essentially, I recommend trying amplifiers from manufacturers known for producing laid-back components. Iíve had excellent luck building a system around these speakers with components from Rotel, and I have no reason to expect that their power amplifiers would be a bad match for these speakers (and they even make inexpensive, low-power models that still have excellent current driving ability). The tube amps Iíve tried all sound terrific with these speakers. A 35w/ch Dynaco ST-70 is plenty of power to drive a pair to ear-bleeding levels with no problems.

Placement

The other thing that really can bite you and leave a bad impression of these speakers is how you place them. All of Klipschís speakers are designed to be placed closer to the corners than typical designs. I like these best sitting about 1-2í from the left, right, and rear walls. Pull them far out into the room and they donít sound as good. Another things to watch out for is toe-in. Most people angle their speakers so that the drivers are directly facing them. Bad idea here--you want these facing directly forward, with no toe-in rotation toward the center. When pointed right at you, the harshness thatís always waiting around for the unwary comes right out. The off-axis sound is much smoother and more pleasant to listen to. The manual that comes with the speaker has very generic recommendations that recommend toe-in for all their speakers; ignore all of their suggestions. They may very well be true with other models, but with the Forte II they are just plain wrong (current production might have a revised manual that gives better advice).

Donít wait too long...

Two warnings. First, if youíre interested, start moving now. Iím told that the rerelease of these speakers is a temporary thing, and that they are going to disappear again in some indeterminate period of time. Second, I havenít actually had a chance to try out a sample from the current product run. I donít see any design changes, and they seemed to sound about the same during a brief listen at the local dealer, but Iím not 100% certain these are exactly the same speakers Iím used to. Even if I had a pair, I couldnít tell you for sure for a while--it took me six months to get my old pair broken in properly (you really have to move that woofer around to stretch the cone and radiator out to get the bass going as deep as it should). The bass does take a while before it sounds exactly right, and the volume level required to break these in right is enough to get your average dealer evicted if they tried it in the store.

As far as Iím concerned, the Forte II is a terrific design competitive with any speaker in the $1000 price class is every category. And they are possibly the best available in terms of deep bass output, sensitivity, and maximum output for that much cash. If you give them a fair audition, following the suggestions I gave for matching components and room placement, you may just find that inexpensive horn speakers can sound better than you thought possible.

.....GS